SOME of Julia Gillard's backers have turned on Bill Shorten, accusing him of using "weasel words" and saying his support for the PM has been weak because he has not declared he would refuse to serve as a minister under Kevin Rudd.

But one of Mr Shorten's allies has fired back, saying: "Bill's not in the Julia party or the Kevin party, he's in the Labor Party. He hasn't invented these problems."

They said Mr Shorten played a crucial role in helping Ms Gillard topple Mr Rudd three years ago and then fighting off two other comeback attempts. They insisted he remained firmly in the PM's camp, despite massive pressure on him to switch sides.

Mr Shorten repeatedly declared yesterday that he supported Ms Gillard. "I will continue to support Julia Gillard to be elected as the next prime minister," he said.

As tensions rise in government ranks about the leadership, those wanting Mr Rudd to return as PM believe resistance will crumble if Mr Shorten gives his "psychologically important" support.

Some of the PM's supporters say they will not make a move unless Mr Shorten does. Others say Mr Shorten cannot be trusted. They say his backing for the PM is not strong enough and he is hedging his bets to look after himself.

Mr Shorten played a key part in toppling Kevin Rudd's leadership three years ago.

One of Mr Shorten's allies said "he's not going to trigger anything", and suggested if it there were a leadership ballot Mr Shorten would almost certainly vote for Ms Gillard.

Mr Rudd yesterday told Channel 7's Sunrise program "I don't believe there are any circumstances" under which he would return as Labor leader -- noticeably different to his pledge in March that there were "no circumstances".

Resources Minister Gary Gray yesterday seized on Mr Rudd's language to dare him to challenge, saying he was causing public confusion and it was time to "put up or shut up".

"I genuinely think that if Kevin Rudd wishes to challenge, he should do so. He should stop this confusion and the mumbling and the mumbo jumbo," Mr Gray told the ABC. "He doesn't have the courage and the strength that's required to do this job. What he can do is spread confusion, what he can do is get himself into the media, what he can do is create torment.

"What he can't do is govern and lead the Labor Party."

Mr Rudd's office replied: "As one of the co-authors of the 2010 leadership coup, it is hardly surprising that Mr Gray has chosen to continue his public attacks on Mr Rudd's character."

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